Waste waters, typically domestic and municipal sewage, contain a variety of contaminants, typically biodegradable suspended, colloidal and dissolved carbonaceous materials, various nitrogenous compounds, including organic nitrogen compounds, ammonia and nitrates, and phosphate materials.
It is relatively simple to remove carbonaceous and phosphate materials from waste water, but rather difficult to remove nitrogenous materials. It is known that it is possible to remove nitrogenous materials biologically or by physical-chemical processes.
One prior art procedure which has been suggested for the biological removal of nitrogenous materials is a three-stage biological system which includes ammonification and nitrification of the nitrogenous materials under aerobic conditions followed by denitrification under anaerobic conditions. The denitrification procedure involves the addition of energy in a chemical form, typically as methanol. This prior art procedure is described by Barth et al in JWPCF vol. 40, No. 12, p.2040 (1968). In this prior art proposal, the treatment process consists of three separate biological sludge systems. Each system has its own recycle and is distinct from the others. The waste water flows through these systems in series, with intermediate settling between the systems. In this way, the biological activities of carbon oxidation to remove carbonaceous materials, ammonification and nitrification and denitrification to remove nitrogenous materials are isolated from each other and occur in three separate stages.
This procedure is successful in the removal of the contaminants, but suffers from several drawbacks. The procedure is time-consuming, results in high net sludge production, has three separate stages of aeration and clarification, and involves considerable control and operating expenditures.